The present invention relates to alkylation of isoparaffin hydrocarbons with alkylating agents in the presence of a strong acid catalyst. Particularly, the invention relates to production of C.sub.7 - C.sub.8 hydrocarbons, suitable for use as motor fuel, by alkylation of isoparaffin hydrocarbon with olefins. More particularly, this invention relates to an isobutane-butylene alkylation process catalyzed by an acid catalyst comprising sulfuric acid and/or flurosulfonic acid containing dissolved carbon dioxide, having high selectivity for production of trimethyl pentanes.
Processes for acid catalyzed alkylation wherein an isoparaffin is reacted with an alkylating agent such as an olefin, alcohol, alkyl sulfate, etc., to form alkyl hydrocarbons are well known. Such alkylation reactions are generally carried out in the liquid phase at temperatures in the range of about 0.degree. - 100.degree. F. and at pressures sufficient to maintain reactants in the liquid phase. Of particular importance is alkylation of isobutane with butylene to form octane hydrocarbons, especially trimethyl pentanes, which are useful as components of motor fuel. The butylenes which may be a mixture of normal and isobutylenes are reacted with a molar excess of isobutane in the liquid phase in the presence of a strong acid such as sulfuric acid, flurosulfonic acid, and mixtures thereof, at temperatures of 0.degree. F. to 100.degree. F. and pressures of 10 to 150 psig, or higher.
The discussion herein is presented with respect to formation of octane hydrocarbons, however, it is to be understood that the discussion is equally applicable to alkylation reactions generally, and particularly to alkylation of isobutane and isopentane with lower molecular weight olefins such as propylene, butylenes, and pentalenes. Basically, it is desirable in an alkylation reaction to promote formation of the 1:1 olefin-paraffin adduct; that is, formation of trimethyl pentanes from butylenes and isobutane.
In strong acid catalyzed alkylation reactions, side reactions occur in which C.sub.12 .sup.+ products are formed as well as the desirable trimethyl pentanes. A portion of C.sub.12 .sup.+ products then undergo cracking to form undesirable lighter hydrocarbons, such as for example, C.sub.5, C.sub.6, and C.sub.7 light alkylate hydrocarbons. The result of such side reactions, then, is to reduce production of the desired C.sub.8 products and to lower the octane number of the alkylate product obtained.